[PATCH 1/2] kvm: use modern cpumask primitives, no cpumask_t on stack

[Rusty Russell]

We're getting rid on on-stack cpumasks for large NR_CPUS.

1) Use cpumask_var_t and alloc_cpumask_var (a noop normally).  Fallback
   code is inefficient but never happens in practice.
2) smp_call_function_mask -> smp_call_function_many
3) cpus_clear, cpus_empty, cpu_set -> cpumask_clear, cpumask_empty,
   cpumask_set_cpu.

Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Mike Travis <travis@xxxxxxx>
---
 virt/kvm/kvm_main.c |   45 +++++++++++++++++++++++++++++++++++----------
 1 file changed, 35 insertions(+), 10 deletions(-)

--- linux-2.6.orig/virt/kvm/kvm_main.c
+++ linux-2.6/virt/kvm/kvm_main.c
@@ -358,11 +358,23 @@ static void ack_flush(void *_completed)
 void kvm_flush_remote_tlbs(struct kvm *kvm)
 {
 	int i, cpu, me;
-	cpumask_t cpus;
+	cpumask_var_t cpus;
 	struct kvm_vcpu *vcpu;
 
 	me = get_cpu();
-	cpus_clear(cpus);
+	if (!alloc_cpumask_var(&cpus, GFP_ATOMIC)) {
+		/* Slow path on failure.  Call everyone. */
+		for (i = 0; i < KVM_MAX_VCPUS; ++i) {
+			vcpu = kvm->vcpus[i];
+			if (vcpu)
+				set_bit(KVM_REQ_TLB_FLUSH, &vcpu->requests);
+		}
+		++kvm->stat.remote_tlb_flush;
+		smp_call_function_many(cpu_online_mask, ack_flush, NULL, 1);
+		put_cpu();
+		return;
+	}
+
 	for (i = 0; i < KVM_MAX_VCPUS; ++i) {
 		vcpu = kvm->vcpus[i];
 		if (!vcpu)
@@ -371,24 +383,36 @@ void kvm_flush_remote_tlbs(struct kvm *k
 			continue;
 		cpu = vcpu->cpu;
 		if (cpu != -1 && cpu != me)
-			cpu_set(cpu, cpus);
+			cpumask_set_cpu(cpu, cpus);
 	}
-	if (cpus_empty(cpus))
+	if (cpumask_empty(cpus))
 		goto out;
 	++kvm->stat.remote_tlb_flush;
-	smp_call_function_mask(cpus, ack_flush, NULL, 1);
+	smp_call_function_many(cpus, ack_flush, NULL, 1);
 out:
 	put_cpu();
+	free_cpumask_var(cpus);
 }
 
 void kvm_reload_remote_mmus(struct kvm *kvm)
 {
 	int i, cpu, me;
-	cpumask_t cpus;
+	cpumask_var_t cpus;
 	struct kvm_vcpu *vcpu;
 
 	me = get_cpu();
-	cpus_clear(cpus);
+	if (!alloc_cpumask_var(&cpus, GFP_ATOMIC)) {
+		/* Slow path on failure.  Call everyone. */
+		for (i = 0; i < KVM_MAX_VCPUS; ++i) {
+			vcpu = kvm->vcpus[i];
+			if (vcpu)
+				set_bit(KVM_REQ_MMU_RELOAD, &vcpu->requests);
+		}
+		smp_call_function_many(cpu_online_mask, ack_flush, NULL, 1);
+		put_cpu();
+		return;
+	}
+
 	for (i = 0; i < KVM_MAX_VCPUS; ++i) {
 		vcpu = kvm->vcpus[i];
 		if (!vcpu)
@@ -397,13 +421,14 @@ void kvm_reload_remote_mmus(struct kvm *
 			continue;
 		cpu = vcpu->cpu;
 		if (cpu != -1 && cpu != me)
-			cpu_set(cpu, cpus);
+			cpumask_set_cpu(cpu, cpus);
 	}
-	if (cpus_empty(cpus))
+	if (cpumask_empty(cpus))
 		goto out;
-	smp_call_function_mask(cpus, ack_flush, NULL, 1);
+	smp_call_function_many(cpus, ack_flush, NULL, 1);
 out:
 	put_cpu();
+	free_cpumask_var(cpus);
 }
 
 

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